1. Field of the Invention
The present invention generally relates to a stationary induction apparatus for transmitting or supplying electromagnetic energy through electromagnetic induction, and more particularly, to a high-frequency heating apparatus to which is applied a technique to electromagnetically shield the power supply side of the stationary induction apparatus (primary side) from the power receiver side (secondary side), without detracting from the electromagnetic induction function therebetween.
2. Description of the Prior Art
Due to the recent progress in inverter technology, an inverter source system is now being put into practical use. According to this inverter source system, commercial frequencies are, before being boosted by a boosting transformer and added to a magnetron, converted into high frequencies. Therefore, if the inverter source system is applied to an electronic oven, a power source of the magnetron of the electronic oven can be rendered compact in size, light in weight and low in manufacturing cost.
Attempts have been made to construct such a microwave generating device for use in an electronic oven (a high frequency heating apparatus) that is light in weight and compact, wherein the primary side coil (power supply side induction element) of the boosting transformer (stationary induction apparatus) is positioned outside a shield casing, while the secondary side coil (power receiver side induction element) is placed inside the shield casing of the magnetron, so that the primary side coil and the secondary side coil are inductively coupled to each other to function as a transformer, and wherein the primary side coil and the secondary side coil are separated from each other by the shield casing, thereby to maintain the shielding function of the shield casing.
In the electronic oven using the above-described system of the inverter power source, the high frequency waves of several tens of KHz produced in the inverter circuit can be advantageously utilized as they are for induction heating. Therefore, if a heating coil for induction heating is added to the electronic oven employing the inverter power source, and the power is arranged to be supplied from the common inverter power source either to the heating coil or to the microwave generating device, an electronic oven equipped with the function of an electromagnetic cooking apparatus which can serve both as an electronic oven and as an electromagnetic cooking apparatus will be brought into the market. In this case, although it may be possible to install the heating coil for electromagnetic cooking on the upper surface of the body of the electronic oven, it will be more convenient to place the heating coil at the bottom, inside the heating chamber, of the electronic oven, so that the room of the heating chamber can be a common space for an object to le heated by the electronic oven and by the electromagnetic cooking apparatus. However, if the heating coil is placed within the heating chamber where the microwave is irradiated, the exciting coil should be protected from damages caused by the microwave, and for this purpose the exciting coil is necessary to be shielded from the microwave, while the exciting coil which is an induction element at the power supply side is necessary to be inductively coupled to a metallic pan or the like (an object to be heated) which corresponds to an induction element at the power receiver side.
Both in the above-described microwave generating device and in the electronic oven functioning also as an electromagnetic cooking apparatus, the electromagnetic waves should be shielded between the power supply side and the power receiver side, but, the high-frequency power of several tens of KHz should be transmitted through electromagnetic induction between the power supply side and the power receiver side. The above-described shielding and transmission of electromagnetic energy are contradictory from a physical viewpoint, and accordingly conventional techniques could not realize such ideas as the above microwave generating device or the electronic oven with the electromagnetic cooking apparatus.